Disease and injury to the anterior surface of the eye are the leading causes of visits to physicians for medical eye care in the United States. These diseases and injuries rank among the most painful of eye conditions and can lead to disability and blindness. Major clinical problems of the surface of the eye include ocular surface drying, tear film abnormalities, and related complications; ocular surface wounds with resultant pathology and scarring; corneal dysfunction dystrophies and inherited disease; inflammatory disease; and external ocular infections. Eye diseases and injuries can have symptoms ranging from itchy, runny eyes to impaired vision. Therefore, it is important to address eye problems right away, as some diseases can progressively worsen or even trigger other serious problems. Most pharmacologic management of ocular disease includes the topical application of solutions to the surface of the eye as drops. Despite the relatively small proportion of a topically applied drug dose that ultimately reaches anterior segment ocular tissues, topical formulations remain effective, largely because of the very high concentrations of drugs that are administered.
Disease and injury to tissues of the posterior segment of the eye, including the retina and choroid, is involved in many of the most common blinding diseases in the industrialized world. Age-related macular degeneration (AMD) alone impacts more than 10 million Americans. Severe vision loss from AMD and other diseases affecting the posterior segment, including diabetic retinopathy, glaucoma, and retinitis pigmentosa accounts for most cases of irreversible blindness world wide. Currently, the treatment of posterior segment disease is to a significant extent limited by the difficulty in delivering effective doses of drugs to target tissues in the posterior eye.